1. Field of the Invention
The description below relates to flexible thermoelectric circuits.
2. Description of the Related Art
Present Thermoelectric Modules (TEMs) use substrates to form the electrical paths to connect individual Thermoelectric Elements (TEEs). Generally, the connections are made so that one surface of an array of TEEs is heated and the opposite surface is cooled when current is passed through the array in a specified direction. Most TEMs have ceramic substrates with copper circuits to connect individual TEEs. The TEEs are soldered to the copper circuits. Other systems use printed and fired conductive ink circuits, and still others use circuits fabricated within the substrate structure itself and have the circuit pattern formed into a monolithic substrate/conductor structure.
In certain TEMs, Kapton or other high temperature organic substrates are used in combination with laminated or deposited copper circuit material. Such assemblies are processed using printed circuit technology to form the circuit pattern and electrically connect the TEEs. The substrate construction produces TEMs that are essentially rigid.
In TEM designs the substrates are on opposite sides of the TEEs forming a sandwich with the TEEs between the substrates. Because of this geometry, present substrates, even those that are polymer based, do not allow the TEM to flex to the degree needed. Furthermore, when such assemblies are bent forcefully, high shear forces are produced on individual TEEs which cause immediate failure or reduced life. In applications that involve exposure to thermal cycling, variable mechanical loadings, shock or vibration, bending and shear forces can occur repeatedly so the systems tend to have short life and can thereby make the use of TEMS impractical
Certain recent applications for TEMs benefit from the use of flexible TEMs that can be shaped to meet the geometrical constraints imposed by the optimized cooling and heating system performance. By employing such flexible TE systems, costs, size and complexity can be reduced and system capability improved.
Substrates are designed and constructed so that they can flex in one or more directions; the construction of such substrates follows certain design guidelines that are described in text and figures that follow. Several variations are described that can meet specific design needs such as (1) flexure in one and more than one direction; (2) designs for TEMs that flex and have zones that heat and others that cool on the same substrate surface; (3) systems that provide thermal isolation in accordance with co-pending U.S. patent application Ser. No. 09/844,818 entitled Improved Efficiency Thermoelectrics Utilizing Thermal Isolation; and (4) systems that are cascades or multi-layered.
Several embodiments and examples of thermoelectrics are described. A first embodiment involves a flexible thermoelectric that has a plurality of thermoelectric elements and first and second substrates. The substrates sandwich the plurality of thermoelectric elements and have electrical conductors that interconnect ones of the plurality of thermoelectric elements. At least one of the first and second substrates is constructed of a substantially rigid material, and the substrates are configured to flex in at least one direction.
For example, at least one substrate may be weakened, have cuts, be formed in sections, be shaped, be constructed of a material, or be modified in order to permit flexing. The flexible thermoelectric, in one embodiment, is for use with a fluid flow, and the sections or cuts are formed in a manner to improve thermal isolation from section to section in at least the direction of fluid flow. Other features may be provided to provide thermal isolation in the direction of fluid flow.
In one embodiment, the thermoelectric flexes in at least two directions. In another embodiment, the thermoelectric is constructed with a single layer of thermoelectric elements, and cools on a first side and heats on a second side, in response to an electrical current. Alternatively, or in addition, at least portions of the thermoelectric may have multiple layers of thermoelectric elements. In this manner, a first plurality of thermoelectric elements may be positioned along a first side of a central substrate and a second plurality of thermoelectric elements may be positioned along an opposing side of the central substrate. The first plurality of thermoelectric elements are sandwiched between the first substrate and the central substrate, and the second plurality of thermoelectric elements are sandwiched between said second substrate and the central substrate. In this embodiment, the flexible thermoelectric may be configured to provide both heating and cooling on one side of the thermoelectric, in response to a current flow.
In one embodiment, the flexible thermoelectric further has at least a first thermal conductor configured to provide heat flow to and/or from the thermoelectric. In addition, the thermal conductor strengthens the thermoelectric.
Another example of a flexible thermoelectric has a plurality of thermoelectric elements, and first and second substrates sandwiching the plurality of thermoelectric elements, wherein at least one of the first and second substrates is constructed in sections in a manner to permit flex of the thermoelectric in at least one direction.
At least one of the substrates may be weakened, formed in sections, have cuts, be of a material selected, or be shaped, to permit flexing. As with the previous embodiment, the flexible thermoelectric may be for use with a fluid flow, and the cuts may be formed in a manner to improve thermal isolation from section to section in at least the direction of fluid flow. In one advantageous embodiment, the flexible thermoelectric flexes in at least two directions.
Again, the flexible thermoelectric may also be constructed with a single layer of thermoelectric elements, or multiple layers of thermoelectric elements. The flexible thermoelectric may be configured to cool on a first side and heat on a second side, or to both cool and heat on the same side. For example, a first plurality of thermoelectric elements may be positioned along a first side of a central substrate and a second plurality of thermoelectric elements may be positioned along an opposing side of the central substrate, where the first plurality of thermoelectric elements are sandwiched between the first substrate and the central substrate, and the second plurality of thermoelectric elements are sandwiched between said second substrate and the central substrate. A thermal conductor may be provided for heat flow to and/or from the thermoelectric. In addition, a thermal conductor may be used to strengthen the thermoelectric.
In another embodiment, a flexible thermoelectric has a plurality of thermoelectric elements, and first and second substrates sandwiching the plurality of thermoelectric elements. In this embodiment, preferably, at least one of the first and second substrates is constructed in a non-uniform manner to permit flex of the thermoelectric in at least one direction. For example, at least one substrate is weakened in places, is formed in sections, has cuts in a plurality of locations, is shaped non-uniformly, or is formed of a material in certain locations in order to permit flexing. Where the thermoelectric is for use with a fluid flow, the cuts or sections or non-uniformities are preferably formed in a manner to improve thermal isolation in at least the direction of fluid flow. In one embodiment, the thermoelectric flexes in at least two directions.
The thermoelectric may be constructed with a single layer of thermoelectric elements, or with multiple layers of thermoelectrics. In this manner, the thermoelectric may be configured to cool on a first side and heat on a second side, and/or provide both heating and cooling on the same side. For example, a first plurality of thermoelectric elements may be positioned along a first side of a central substrate and a second plurality of thermoelectric elements may be positioned along an opposing side of the central substrate, the first plurality of thermoelectric elements sandwiched between the first substrate and the central substrate, and the second plurality of thermoelectric elements sandwiched between said second substrate and the central substrate.
A method of constructing a flexible thermoelectric is also disclosed, involving the steps of providing a plurality of thermoelectric elements, and positioning or forming the thermoelectric elements between first and second substrates, wherein at least one of the substrates is constructed of a substantially rigid material, and configured to permit flexing of the thermoelectric.
In accordance with the method, the substrates may be formed in sections, may be weakened in locations, may have cuts, may be shaped, and/or may be formed of material selected to permit flexing in one or more directions. Where the resulting thermoelectric is for use with a fluid flow, the method involves making the thermoelectric in a manner to improve thermal isolation in at least the direction of fluid flow.
The method may involve forming a single layer of thermoelectric elements, or multiple layers of thermoelectric elements. In this manner, the thermoelectric may be configured to provide heating on one side and cooling on another, and/or both heating and cooling on the same side.